December 5-6, 2020 Storm Observations and Nowcast

[Ginx snewx]

Rain totals

[It's Always Sunny]

I know I'm speaking for others but events like these always leave a dent in forecasting confidence because there have been many times where the best lift wasn't quite in the DGZ but still yielded great amounts and then you have yesterday's storm that pretty much puts us back in check. I remember earlier this year (I forget the date Will probably knows lol) but mid level dry air was a potential issue which made many of us poo-poo it but most of SNE ended up doing really well. If I can find the date I'll update this post but point being that was a storm that left a dent as well.

EDIT: December 11, 2019 event with the mid-level dry pocket.

[OceanStWx]

13 minutes ago, mahk_webstah said:

Point taken.  It still seems like there are more misses these days and model gyrations.  It is not just the maps because you help us see reality.  The Euro no longer dependable, gfs kinda new.  It all just seems less can be counted on from models these days although maybe it is the bias that comes from paying attention more.  It wouldn’t surprise me though that the pace of climate change fooks with the analogue data; Tip has talked about this.  I’m not a scientist so can’t provide any reliable analysis.  But if the Mets don’t feel the models are worse with these storms, then you are probably right since you work with them every day.

It's not worse, just different.

15 years ago when I was in school, models were all 80 km resolution. You would have to tease out banding potential and snowfall forecasts were more broad, with "locally higher amounts". 

Now models are finer resolution which is prone to more wobbling when they can resolve features down to 9 or 13km. Banding doesn't need to be teased out, but can be modeled, and "locally higher amounts" are explicitly forecast by guidance. So when those shift around it's far more noticeable.

[WinterWolf]

1 minute ago, It's Always Sunny said:

I know I'm speaking for others but events like these always leave a dent in forecasting confidence because there have been many times where the best lift wasn't quite in the DGZ but still yielded great amounts and then you have yesterday's storm that pretty much puts us back in check. I remember earlier this year (I forget the date Will probably knows lol) but mid level dry air was a potential issue which made many of us poo-poo it but most of SNE ended up doing really well. If I can find the date I'll update this post but point being that was a storm that left a dent as well.

Good points.  It goes both ways, sometimes we poo poo something and it still works out well because something offset the potential issue.  
 

And sometimes we see the issues and feel this or that should overcome the issue, and it doesn’t.   It’s not an exact science yet....humbling to say the least.  Looking forward to the next threat. 

[It's Always Sunny]

1 minute ago, WinterWolf said:

Good points.  It goes both ways, sometimes we poo poo something and it still works out well because something offset the potential issue.  
 

And sometimes we see the issues and feel this or that should overcome the issue, and it doesn’t.   It’s not an exact science yet....humbling to say the least.  Looking forward to the next threat. 

Yeah exactly to your point.  Like you said events that don't look so hot then do great, we pick out what went well, what overproduced, etc and we do the opposite for when we have high expectations and it doesn't materialize.

[STILL N OF PIKE]

If post 20z the winds at 850-925 veering to NNW..didn’t seem to effect the QPF that much ..could they have been responsible for a slight moderating of low level temps (via downsloping)  when they turned this direction for Central mass over to S NH and why elevation maybe played a even bigger part  than forecast for second half . 
 

BC Nashua was like 32.5 mid day and then 33.5 34 late pm and evening . 

[It's Always Sunny]

4 minutes ago, STILL N OF PIKE said:

If post 20z the winds at 850-925 veering to NNW..didn’t seem to effect the QPF could they have been responsible for a slight moderating of low level temps (via downsloping)  when they turned this direction for Central mass over to S NH and why elevation maybe played a even bigger part  than forecast for second half . 
 

BC Nashua was like 32.5 mid day and then 33.5 34 late pm and evening . 

Maybe so but that would probably happen more often during similar setups if that were the case.  Others will likely add onto this but I think it goes back to the lack of lift in the DGZ.

[wxsniss]

5 hours ago, CoastalWx said:

The weenie maps just don’t take anything important really into consideration. I hate them lol. I thought it would pound in metro west, but it did not. I do think the lift into the DGZ was only confined to a narrow area associated with the higher terrain coincidentally (I think I even said it’s possible this could be a storm that really differs from low elevation to high elevation). Therefore if it doesn’t pound dendrites, it is tough to latent cool to near 32. That’s probably a big reason. If I was on air or a NWS met, I would have busted there for sure. Hell I busted on 1-3 for BOS lol. Congrats on the little one!

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, lack of drier dewpoints, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

[ORH_wxman]

2 minutes ago, wxsniss said:

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

The lift was lowering throughout the event over E MA. There was prob more DGZ lift during the initial changeover than later on...maybe Chris or someone has easier access to the cross sections than I do at the moment, but I’m pretty sure i recall seeing the lift a bit deeper earlier in the event. 

Usually once you flip over to snow, keeping excellent DGZ isn’t a huge deal because your in the CCB and often advecting cold air into the system...but this was a unique system in which we were not so the issue ended up more glaring than it usually would be. 

[OceanStWx]

1 minute ago, wxsniss said:

Thanks man!

Great disco here between you, Will, Tip, OceanStWx, and others... 

One question that's been bugging me because I'm sure the answer is simple:

All the red flags granted --- lift way lower than DGZ, DGZ so high up that there's a longer 32F path of descent and the "snow" is more ready to melt, garbage airmass --- but none of these were an issue during the changeover. I made a timelapse (I can't figure out how to upload) showing we went from rain bare ground to white coating on most surfaces in < 5 min! And people everywhere metrowest down to northeast CT were reporting the same.

At 4pm, extrapolating that for the next 4+ hours, even if intermittent, it looked like much of eSNE would easily reach the NWS totals as the bands pivoted.

Anyone know why was that 30 min period during the changeover able to overcome all the red flags, in contrast to the subsequent 4+ hours?

Most likely answer is that when the changeover occurred the thermodynamic profile didn't look like what we've described. The DGZ was likely lower in the atmosphere, and over time the WCB forced it to rise. Those mid level temps were way colder at 12z (despite surface temps being near 40) than they were at 00z (despite surface temps being near 33).  

[CoastalWx]

Just now, OceanStWx said:

Most likely answer is that when the changeover occurred the thermodynamic profile didn't look like what we've described. The DGZ was likely lower in the atmosphere, and over time the WCB forced it to rise. Those mid level temps were way colder at 12z (despite surface temps being near 40) than they were at 00z (despite surface temps being near 33).  

Yeah and over time the DGZ dried out after it flipped, at least that’s what I noticed when I was looking at BOS. Radar started to shred a little. I think it was thumping good in those areas in metro west shortly after changeover and then went to crap after the DGZ rose and dried out a bit.

[OceanStWx]

Check out the GYX evolution. Whole sounding (including the DGZ) moves up and to the right, indicative of WAA (which you can see in one of the middle columns "inferred temp advection"). Right after the flip to snow you probably only had a 1-1.5km deep near freezing layer vs 3km later.

[ORH_wxman]

5 minutes ago, CoastalWx said:

Yeah and over time the DGZ dried out after it flipped, at least that’s what I noticed when I was looking at BOS. Radar started to shred a little. I think it was thumping good in those areas in metro west shortly after changeover and then went to crap after the DGZ rose and dried out a bit.

Yeah you’re left with like these -5C needles falling into that deep 32-33F layer. Not a good combo for efficient accumulation is an understatement. 

[Damage In Tolland]

This may be the only time we see something like this , this winter .

 

[CoastalWx]

LOL October keeping me above climo for now. 

[PhineasC]

Deep winter feel in Randolph. 

[WinterWolf]

9 minutes ago, CoastalWx said:

LOL October keeping me above climo for now. 

Hey..whatever it takes lol. 

[WinterWolf]

3 minutes ago, PhineasC said:

Deep winter feel in Randolph. 

Phin, are you on the east side of the whites/presidentials? 

[Baroclinic Zone]

9 minutes ago, WinterWolf said:

Phin, are you on the east side of the whites/presidentials? 

North

[PhineasC]

But the lodge is cozy. 

[ORH_wxman]

This crap was like slime and then froze overnight. Back in holliston we got about 4” of Italian ice. But the piles make it look like double that because of the water content. 

[STILL N OF PIKE]

6 minutes ago, PhineasC said:

But the lodge is cozy. 

You are the New Caretaker at the beautiful Overlook ..view 

[tamarack]

After seeing nearby cocorahs reports I can't be too critical of snow total verification.  Chesterville, 7-8 miles to my SW, reported 2.9" from over 2" total precip, not quite half my 6.0 and with considerably more precip.  12 miles to my WSW, the Temple observer at 1220' had 11.5".  3 stations, all within less than a 30 minute drive from each other, and a 1-2-4 ratio of snowfall.  

[wxsniss]

Yeah I see it now, thanks all, it really was that simple.

The changeover had transiently good lift through the DGZ, I guess enough to cool soundings to keep it snow thereafter. But lift dropped and stayed low while we were supposed to be rocking in a comma head.

These are from 12z 3k NAM, before (21z), ~during (00z, I know in reality changeover was around 21z), and after (02z):

[HoarfrostHubb]

1 hour ago, Ginx snewx said:

Rain totals

Wow   8.5" on 1.6ish precip... some was straight rain, but not a lot here.  Prob 1.5" was snow... so 5.7 : 1 ratio cement

[wdrag]

Hi.  My wrap addition.    Added snow reports that were accepted by the NWS and the lightning archive. 

While one can argue on the use of models and models vs pattern recognition, one difficulty continues over the years... use of 10 to 1 snow ratios. We need to be careful about this. NWS has a blended snow ratio tool (every 6 hours or less which can be interpolated). Overall model intent was good (except the one day of  a very westward set of solutions) but model snowfall was way overdone on amounts Southern NH southward that performed  the phase change reasonably well (NAM/EC).  The over-forecast was probably due to the occurrence of wet snow during 33-34F air temp, non frozen ground and much of it during daylight hours. My guess (there may be some verification out there?) was a 6 to 1 snow water ratio (if someone can provide some documentation on ratio-that would be helpful)?  This especially since many folks were speaking or imaging large flakes (DGZ ideal or less than ideal).

Snow accumulation may have as much or nearly as much to do with ratios as DGZ.   I always start with total positive snowfall change, then check the usually heavier Ferrier, and then IF frozen ground and lower thicknesses below 5380 DM - I will look to as much as 10 to 1 or Kuchera.  These are painfully earned considerations over my life.  

I may be wrong on Kuchera... but my guess is Kuchera does not take into account 33F melting that was modeled in the EC 2m temps?  Maybe it does... Sometimes Kuchera works excellent, but my experience is that it is best when clearly the sounding does not allow any melting or wet snowflakes (colder scenarios). 

Hopefully this makes sense.  I'm open to better science- if you have it, please add it (I do not have BUFKIT). 

 

My second thoughts and CT did add something recently on this...  This elevation snowstorm (event?) while not the biggest ever (never was supposed to be), not only placed ORH a foot temporarily ahead of normal, the daily record setting 9.6" was also about 14-15% of the climate 1981-2010 normal.   Since the general thinking here our forum and elsewhere, is a La Nina winter and below normal snowfall... it may be that ORH received 20% of it's seasonal total (normal is 64.1")????? I don't know.  

Whether we may have paid too much attention to yesterdays storm,  it was probably an important one for this winter at ORH.  I fervently hope that I'm wrong and we don't look back at this early Dec snowstorm, as the biggie (like last cold seasons Dec 1-2 event).  

arghhhh 

[Lava Rock]

Very elevation dependent storm. At 300' only a few inches of snow and nothing on trees. Up by our house at 730', big difference. Lots of birch benders. Last pic is Long Lake, Naples

[Damage In Tolland]

10 minutes ago, wdrag said:

Hi.  My wrap addition.    Added snow reports that were accepted by the NWS and the lightning archive. 

While one can argue on the use of models and models vs pattern recognition, one difficulty continues over the years... use of 10 to 1 snow ratios. We need to be careful about this. NWS has a blended snow ratio tool (every 6 hours or less which can be interpolated). Overall model intent was good (except the one day of  a very westward set of solutions) but model snowfall was way overdone on amounts Southern NH southward that performed  the phase change reasonably well (NAM/EC).  The over-forecast was probably due to the occurrence of wet snow during 33-34F air temp, non frozen ground and much of it during daylight hours. My guess (there may be some verification out there?) was a 6 to 1 snow water ratio (if someone can provide some documentation on ratio-that would be helpful)?  This especially since many folks were speaking or imaging large flakes (DGZ ideal or less than ideal).

Snow accumulation may have as much or nearly as much to do with ratios as DGZ.   I always start with total positive snowfall change, then check the usually heavier Ferrier, and then IF frozen ground and lower thicknesses below 5380 DM - I will look to as much as 10 to 1 or Kuchera.  These are painfully earned considerations over my life.  

I may be wrong on Kuchera... but my guess is Kuchera does not take into account 33F melting that was modeled in the EC 2m temps?  Maybe it does... Sometimes Kuchera works excellent, but my experience is that it is best when clearly the sounding does not allow any melting or wet snowflakes (colder scenarios). 

Hopefully this makes sense.  I'm open to better science- if you have it, please add it (I do not have BUFKIT). 

 

My second thoughts and CT did add something recently on this...  This elevation snowstorm (event?) while not the biggest ever (never was supposed to be), not only placed ORH a foot temporarily ahead of normal, the daily record setting 9.6" was also about 14-15% of the climate 1981-2010 normal.   Since the general thinking here our forum and elsewhere, is a La Nina winter and below normal snowfall... it may be that ORH received 20% of it's seasonal total (normal is 64.1")????? I don't know.  

Whether we may have paid too much attention to yesterdays storm,  it was probably an important one for this winter at ORH.  I fervently hope that I'm wrong and we don't look back at this early Dec snowstorm, as the biggie (like last cold seasons Dec 1-2 event).  

arghhhh 

Around NE CT here it was 3.75:1 ratio

 

[Whineminster]

3 hours ago, Damage In Tolland said:

What’s your elevation there? That looks up there . Is that Wachusett in background?

Just under 1,100'.  Yeah that's wachusett. My pack retention isn't great though do to my south exposure. 

[STILL N OF PIKE]

At ASH , we got 1 inch QPF After 2pm and it led to maybe an inch of snow for a 1:1 ratio as it was 98% snow lol

 

At Miller state park they had well over a foot at  1600’  (got a settled depth of just over 13”) around that elevation . Much above that was impossible  to measure as less trees and serious blowing and drifting on exposed NW spots